The Pokémon Company has received a number of questions about how the QR Codes are associated with Rental Teams and Friendly Competitions on the Pokémon Global Link (PGL), and about an error that sometimes occurs when they are read. The QR Codes are unique to your version of the Pokémon Sun or Pokémon Moon game you have registered at the PGL, so if you attempt to read a QR Code given to you from another Trainer, it will not work. Be sure to log in to the PGL and use your own Pokémon Sun or Pokémon Moon game to scan the QR Code for yourself to avoid any errors. For more information about this, visit the official QR Rental Team support page.
Source: Pokémon Global Link
Pokémon Blog 
One thought on “Pokémon Sun and Moon: Rental Team and Friendly Competition QR Codes cannot be shared”